mkexp: changed 'list' filter replacement to map the empty string to an empty list. Added option to keep empty string as singleton list if needed

mkexp: reading of EXP_DESCRIPTION from initial comment now also discards leading and trailing lines that only contain white space and comment characters

mkexp: added work-around for Jinja 2.8 bug when applying eval_ctx filters to literals (eval_ctx and value are swapped)

mkexp: fixed missing mkdir -p option in cppath to allow incremental copying of data that is not produced in one go